Image MIME Reference
PNM
Portable Anymap
image/x-portable-anymap
VS
AutoCAD Slide
image/vnd.sld
SLD
A complete technical comparison of Portable Anymap and AutoCAD Slide — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | PNM | SLD |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
Portable Anymap
image/x-portable-anymap
Extension
.pnm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (PBM), 8-bit to 16-bit (PGM), 24-bit to 48-bit (PPM)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 31, 50 32, 50 33, 50 34, 50 35, or 50 36
AutoCAD Slide
image/vnd.sld
Extension
.sld
Container
AutoCAD Slide Container
Compression
Uncompressed (Vector Instructions)
Algorithm
None
Color Depth
8-bit (AutoCAD Indexed Color)
Developed by
Autodesk, Inc.
Released
1980s
Magic Bytes
41 75 74 6F 43 41 44 20 53 6C 69 64 65 0D 0A 1A 00
Browser Support Comparison
| Browser | PNM | SLD |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
PNM
PNM Strengths
- Unparalleled simplicity: parsers and writers for PNM files can be written from scratch in C or Python in just a few minutes without relying on external libraries
- Serves as an excellent foundational teaching tool for computer science students learning about image arrays and raster graphics
- Flawlessly pipes through Unix command-line utilities for robust automated image processing (via the Netpbm suite)
Limitations
- Zero compression natively results in astronomical file sizes, making it entirely impractical for web delivery or consumer storage
- No support for standard metadata formats like EXIF, XMP, or ICC color profiles
- No native alpha channel support in the classic PNM specification (though the newer PAM format 'P7' addresses this)
SLD
SLD Strengths
- Allowed for instantaneous loading of highly complex architectural and engineering blueprints on low-memory MS-DOS systems
- Easy-to-parse binary structure containing simple opcodes for drawing vectors and polygons
Limitations
- Completely obsolete and heavily fragmented, largely replaced by PDF and lightweight web-based DXF viewers
- Destructive 'snapshot' format irrevocably strips all useful, editable CAD geometry data from the original drawing
- Zero support in web browsers or standard image processing libraries
When to choose which format
PNM
Use PNM when…
- Unix/Linux Command-Line Image Processing (Netpbm suite)
- Academic Computer Vision Research
- Intermediary Format for Image Format Conversion
SLD
Use SLD when…
- Legacy AutoCAD Slideshows
- AutoCAD Custom Icon Menus
- Historical CAD Archival